PREDILATING WIRE FOR ANGIOPLASTY

Abstract: A predilating wire (10) is provided for use in coronary angioplasty with a separately passed balloon catheter (20). The wire has a flexible distal tip portion (12) of minimum diameter followed by a tapering frusto-conical enlarged portion (16) which tends to open an occluded artery through which the wire is passed. A separately passed catheter threaded onto the guide wire has a balloon (20) of similar diameter when collapsed to the larger end of the enlarged portion (16) which can protect and guide the catheter into its final position ready for use.

Description: PREDIIATING WIRE FOR ANGIOPLASTY This invention relates to a predilating wire for use in the treatment of stenotic or occluded arteries, particularly coronary arteries or by-pass grafts. Current coronary angioplasty systems consist of a steerable guide wire, a guiding catheter, and a balloon catheter. The essence of the technique is to cross the stenotic or occluded segment of a coronary artery or by-pass graft firstly with the guide wire, followed by the balloon catheter. The system is deployed from the guiding catheter and manoeuvring of the guide wire is performed under x-ray screening. Despite improvements in guide wire and balloon catheter design and construction, failure to cross the stenotic or occluded segment either with the wire, or more commonly with the balloon, occurs in 5 to 10% of cases, depending upon the anatomy of the coronary vessel and the severity of the stenotic narrowing. It is known to provide a balloon catheter guide wire with a spherically rounded distal tip of larger cross-section (typically 1 mm) than the remainder of the guide wire (typically 0.6 mm). However, such a design requires a considerable initial force to cross the stenotic or occluded segment of the artery initially. The rounded, enlarged tip is in fact more likely to jam than the slender tip of a conventional guide wire. Further, the stiffness of the distal tip of the wire makes it more difficult to manoeuvre into position. It is an object of the present invention to provide an improved design of guide wire which can facilitate successful crossing of the stenotic or occluded arterial segment by both the guide wire and the balloon catheter. It has been proposed in 092/13589 to use a balloon catheter of a single lumen type having a guide wire which is of tapering form, the extreme distal tip of the guide wire having a hemispherical enlarged tip and a spherical valve member spaced from the extreme tip which can be drawn back against the distal end of the balloon. The spherical valve member seals the distal end of the balloon so that the single lumen can be inflated. The guide wire has a tapering form with the hemispherical tip and spherical valve member being provided on the thinnest portion, a slightly thicker portion passing through the balloon, and a thicker portion extending to the proximal end of the assembly. This tapering construction of the guide wire means that the balloon has to be kept close to the extreme distal tip of the guide wire since the thick portion of the guide wire will not pass through the balloon. The blunt hemispherical tip also requires initial force to cross a stenotic or occluded segment of artery as referred to above. The assembly lacks manoeuvrability, particularly since the catheter has to be passed with the guide wire, that is the guide wire is not removable from the assembly. According to the present invention, there is provided a guide wire which is constructed and adapted to guide a balloon catheter to a desired position in an artery, said guide wire having a distal end region including a distal tip of minimum cross-section and a portion of enlarged cross-section at a location thereon which is spaced from the distal tip. The enlarged portion is preferably tapered so that the cross- sectional area thereof reduces in the direction of the distal tip. The distal tip may be of smaller cross-section than the remainder of the wire. The distal tip region may be more flexible than the remainder of the wire. The guide wire itself may be constructed in a conventional fashion with a stainless steel mandrel forming the inner core of the wire, and a coating of a non-thrombogenic, smooth polymer layer to facilitate passage of the balloon catheter thereover. The distal tip region of the guide wire may have the mandrel omitted. The proximal end of the enlarged portion may have a diameter which is approximately equal to the minimum un-inflated diameter of a balloon catheter to be used in conjunction with the guide wire. Preferably, the enlarged portion is located a few centimetres, typically about 20 mm to 30 mm, most preferably about 30 mm, from the distal tip. The wire over the length of the distal end region between the distal tip and the enlarged portion may have a greater degree of flexibility than the region of the wire which is on the proximal side of said enlarged portion. The length of the enlarged portion is typically about 3 mm to 6 mm. The guide wire may have a diameter of between 0.25 mm and 0.45 mm. The enlarged portion may taper from the thickness of the wire up to about 1.0 mm in diameter. (The size will be selected to be compatible with the size of the balloon with which it is to be used) The present invention also resides in a balloon catheter assembly comprising a balloon catheter in combination with a guide wire according to the present invention. The balloon catheter may be a twin lumen catheter or a single lumen catheter. It may be of a monorail type. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing in which Fig 1 is a schematic view of a guide wire according to the present invention, and Fig 2 is a schematic view showing use of the guide wire of Fig 1 in conjunction with a balloon catheter. Referring now to Fig 1, the guide wire 10 is of extended length, typically 1500 mm, and is formed of a stainless steel inner core coated with a non-thrombogenic, smooth polymer layer to facilitate sliding movement of the balloon catheter in use. The inner core of the wire tapers at the distal end region 12 and may stop a few centimetres short of the end. The guide wire has a diameter, in this embodiment, of 0.25 mm, although it may have a larger diameter, eg 0.45 mm. The distal end region 12 has a length "a" which in this embodiment is about 30 mm. This distal end region 12 has a flexibility which is greater than the remainder of the guide wire 10 and which is sufficient to enable it to be steered along the desired path. The distal end region 12 terminates in a fine, rounded distal tip 14 having a diameter which is no greater than the remainder of the region 12. In accordance with the invention, the guide wire 10 is provided with a portion 16 of enlarged cross-section defined by a frusto-conically tapering enlarged portion whose diameter decreases towards the distal tip 14 where it merges with that of the wire. The enlarged portion 16 has a length of about 10 mm. The frustum (ie the distal end) of the enlarged portion 16 has a diameter which equals that of the region 12 whilst the base (i.e. the proximal end) of the enlarged portion 16 has a diameter which is equal to up to 1.0 mm in this embodiment. The length of the enlarged portion should be as short as reasonably possible, so as not to reduce the flexibility of the wire too greatly. A suitable length may be 3 mm to 6 mm, and may vary in proportion to the maximum diameter and hence the balloon size, to give a suitable taper angle between about 10° and 40°. In use, the guide wire 10 is inserted into an artery in the leg of a patient having a stenotic coronary artery using a guide catheter and is passed along the artery until the distal tip 14 has passed through the stenosis in the coronary artery. Because the distal tip 14 is of a relatively small diameter, the minimum diameter of the guide wire, this does not require a very large force. In turn, this permits the diameter of the guide wire 10 as a whole to be small since the longitudinal force needed for insertion is low. At this stage, the distal tip 14 lies on the opposite side of the stenosis from the enlarged portion 16. With the guide wire 10 in the above-described position, a balloon catheter comprising a balloon 20 in an un-inflated condition fixed to the distal end of a catheter 22, is inserted into the artery over the guide wire 10 in a manner known per se and slid along the artery until the distal end of the catheter 22 abuts against the base end of the enlarged portion 16 of the guide wire 10 (as shown in Fig 2) . It is to be noted that the diameter of the base of the enlarged portion 16 is approximately equal to the outer diameter of the balloon 20 when in its un-inflated condition. If there is no major resistance to the passage of the wire, the catheter can be brought to the stenotic or occluded segment of the artery and the balloon can then be inflated for use. However, where the artery is heavily diseased, the guide wire can be passed through the stenosis using the manoeuvrability of the relatively soft and very fine tip, the tapered enlarged portion can then be used to slightly open the stenosis until the enlarged portion of the wire itself can be passed through. This opens up the vessel slightly so that it does not damage the relatively soft balloon tip of the catheter. The wire can be slightly withdrawn to position the balloon catheter against the base of the frusto-conically tapering enlarged portion 16 as shown in Figure 2 and locked in position so that the catheter and wire are subsequently moved as a unit through the stenosis to enable the balloon to be deployed. The device therefore allows for a gentle passage of the flexible tip, slight opening up of the stenosis and the subsequent deployment of the balloon without damage to it. Because of the tapering shape of the enlarged portion, the longitudinal force on the wire tends to centralise the device in the occluded artery, making passage of the balloon easier. In a conventional balloon catheter, there is friction to overcome both between the balloon and the occluded arterial wall and between the balloon and the guide wire during passage of the catheter along the wire in fixed position. The latter friction is eliminated if the catheter is locked onto the wire for the final stage of insertion and additionally the wire with its enlarged portion tends to stiffen the balloon against distortion or damage by the arterial wall. However this advantage is accompanied by the advantage of being able to pass the guide wire initially without the catheter being present. It will be appreciated that the enlarged portion 16 protects the balloon 20 against deformation and damage as it is being passed into the stenosis in the artery. The general reduction in the diameter of balloon catheters (to allow the use of smaller bore guiding catheters in order to reduce the size of the arterial puncture) has also led to a reduced strength of the shaft of the balloon catheter. The present invention mitigates this problem by enabling the catheter 22 and wire 10 to be finally advanced as a unit with the enlarged portion 16 forcing a passage through the stenosis. As in conventional systems, the flexible distal end region 12 keeps the parts inside the lumen of the artery with no risk to perforation of the arterial wall. This is particularly important in total or near total occlusion, where traverse of the guide wire itself through the . occlusion does not necessarily result in successful balloon crossing. The guide wire of the present invention can be used with all current balloon catheter systems that employ a freely moveable wire. In addition to designs where the guide wire passes through the total length of the balloon catheter 22, the present invention is also applicable to balloon catheter systems of the so-called "mono-rail" type where the guide wire extends through the balloon catheter for only a relatively short distance behind the balloon before emerging through a hole in the wall of the balloon catheter.

Claims: CLAIMS 1. A guide wire constructed and adapted to guide a balloon catheter to a desired position in an artery, said guide wire having a distal end region including a distal tip of minimum cross-section and a portion of enlarged cross-section at a location thereon which is spaced from the distal tip. 2. A guide wire according to claim 1 wherein the enlarged portion is tapered so that the cross-sectional area thereof reduces in the direction of the distal tip. 3. A guide wire according to claim 1 or claim 2 wherein the distal tip is of smaller cross-section than the remainder of the guide wire. 4. A guide wire according to any preceding claim wherein the distal tip region is more flexible than the remainder of the wire. 5. A guide wire according to any preceding claim comprising a stainless steel mandrel forming the inner core of the wire and the coating of a non-thrombogenic, smooth polymer layer. 6. A guide wire according to claim 5 wherein the distal tip region of the guide wire has the mandrel omitted. 7. A guide wire according to any preceding claim wherein the proximal end of the enlarged portion has a diameter approximately equal to the minimum uninflated diameter of a balloon catheter to be used in conjunction with the guide wire. 8. A guide wire according to any preceding claim wherein the location of the enlarged portion is between 20 mm and 30 mm from the distal tip. 9. A guide wire according to any preceding claim wherein the length of the enlarged portion is between 3 mm and 6 mm. 10. A guide wire according to any preceding claim having a diameter of between 0.25 mm and 0.45 mm on which the enlarged portion tapers from the thickness of the wire up to 1.0 mm in diameter. 11. In combination, a guide wire according to any preceding claim and a balloon catheter.

Inventors: SHIU MAN FAI, SHIU, MAN, FAI
Applicants: SHIU MAN FAI, SHIU, MAN, FAI
Application year: 1994
Main classification: A61M25
IPC codes: A61M29